1. Field of the Invention
This invention relates to a method of drilling and completing a well.
More particularly, this invention relates to a method for placing a means of communication between an injection zone and the well borehole without perforating and gravel packing. The method focuses on improving the reliability over current methods of sand control used in injection wells and will also reduce time, improve safety, and reduce costs.
2. Description of the Related Art
The need for reliable injection well completions crosses industry boundaries. Highly corrosive or toxic industrial wastes from chemical plants, fluids from mining operations, water from hydrocarbon production, and cooling water from power plants can be safely disposed of in subterranean formations. However, the injection well completions these wastes are injected into need to be reliable to ensure the safety of employees, surrounding communities, and the environment. Also, reliability is required to ensure that production of chemicals, minerals, and energy can continue without interruption should an injection well completion failure occur. The cost of a failed injection well can be very high, not just in financial terms, but in terms of human and environmental risk. Because of the tangible and intangible costs associated with an injection well failure, it is important that injection wells be as reliable as possible. Also, it is important to seek ways to reduce the time spent on injection well construction and completion operations to minimize cost. Also, if the number of personnel and the amount of equipment can be reduced during injection well completion operations safety inherently improves.
Many injection zones are by their very nature weak or unconsolidated rock and/or sandstone. These weak formations contain formation particles and other debris which can slough into the well borehole and negatively affect the injectivity of the well. There has been much effort and focus on preventing formation sloughing in production wells. Water wells and hydrocarbon production wells have been the primary focus of study in regard to sand production or formation sloughing. The same means of preventing formation sloughing in production wells have been applied to injection wells throughout the years.
One common method of injection well construction and completion is to install a gravel pack to control formation sloughing. A gravel pack is a two stage filter that consists of a sized screen and sized sand. The sized sand stops sloughing of the formation matrix and the screen keeps the sized sand in place. A typical method would be to drill a borehole with conventional drilling fluids, run casing into the borehole and cement the casing in place, displace the conventional drilling fluids with a clear brine, filter the brine and clean the borehole, run perforating guns in the well and perforate the casing, remove the perforating guns and re-clean the casing, re-filter to the clear brine fluids, run in the well with a gravel pack screen assembly, use high-pressure pumps place sized sand between the sized screen assembly out into the perforation tunnels and against the formation face and filling the annulus between the sized screen and casing. This is a costly, time-consuming process.
There are many disadvantages from the above procedure. These disadvantages can be broken into two categories; equipment and process reliability. There have been instances where leaks have caused perforating guns to low order detonate resulting in no or poor perforating performance and expensive fishing operations to remove the damaged perforating gun bodies. Also, sized screens have failed during the high-pressure pumping operation used to place the sized sand around the screen causing additional fishing operations.
Formation damage is also a problem during injection with this type of injection well construction and completion. Conventional drilling fluids can allow filtrate and solid particles to invade the formation causing restrictions in the productive pore spaces. Another source of formation damage is the shaped charges or explosives used in perforating. The energy from these explosives pushes the casing, cement, and formation aside when creating the perforation tunnel. This causes crushing of the formation matrix reducing the permeability and limiting flow potential of injected fluids into the formation.
Another common method of injection well construction and completion is to drill a borehole and not run casing across the productive formation. This type of well construction is termed barefoot or openhole. The most common practice is to run a sized screen assembly in the openhole section and place sized sand around the screen filling the area between the screen and the formation face. The large increase in formation surface area available to accept fluid in an openhole helps improve injectivity in these types of completions when compared to cased and perforated completions.
In both openhole and cased hole completions the sized screen assembly itself can serve as the restriction in the well borehole. This may cause unnecessary pressure drops which restrict injection. Also, the sized screen may need to be removed for remedial operations. The process of removing an object from a well borehole is called fishing. These operations are costly and time consuming and not always successful resulting in a need to re-drill a portion of, or possibly the entire well. When hazardous wastes have been injected into the well, fishing can prove to be a hazard to the workers, community, and environment. Reliability is a key driver for injection well design and completion.
Keeping in mind that the methods described above were developed for production operations, the question of reliability in injection wells becomes a big issue. In the production environment, the fluid flows from the productive formation, any sloughing or movement of formation material is retained by the sized sand which in turn is retained by the sized screen. This combination yields a reliable means of preventing the formation material from sloughing into the well borehole. However, in the injection mode, fluid moves from the well borehole, through the sized screen, through the sized sand, and into the formation. If the sized sand is pumped away from the sized screen, formation material is free to move into the well borehole through the sized screen. There are several possible mechanisms which would cause the size sand to be displaced from the sized screen.
In both types of completions, openhole and cased hole, formation damage can restrict injection into the well. The may also be times when it is desirable to inject larger volumes of fluids into the well at high injection rates. If the desired injection rate and pressure exceeds the formation fracture pressure, the formation matrix parts and a fissure opens. When the formation is fractured, the surface area of the injection zone increases along the part or fracture face. This allows the fluid to enter the formation at the desired pump in rate. A detrimental side effect of fracturing the formation is that the sized sand, which was placed around the screen as an essential component of the gravel pack filter, is pumped away from the screen into the fissure which developed as the formation matrix is fractured. When this occurs the formation can slough into the well borehole through the sized screen.
Acid is sometimes used in injection wells to improve fluid infectivity into a formation. The acid can, in some cases, dissolve enough of the formation matrix to allow the sized sand to be pumped a way from the screen allowing formation material to enter the well borehole. In some cases the injected fluid being pumped into the well borehole causes a redistribution of the formation matrix which can cause the formation matrix to compact or rearrange in such a manner as to allow the sized sand to be pumped away from the sized screen. Any operation which causes the slightest void in the sized sand can lead to formation sloughing and loss of injectivity into the well.
Devices which eliminate perforating and gravel packing have been introduced for application in hydrocarbon production wells. U.S. Pat. No. 3,347,317 to Zandmer disclosed an extendable duct with solid particles acting as a gravel pack median. WO9626350 to Johnson disclosed an extendable. These devices have not been widely used in hydrocarbon production. These devices trap drilling mud filter cake between the sand control filter media and formation face which limit productivity due to plugging of the formation and filter media. In another invention targeting hydrocarbon production, U.S. Pat. No. 5,425,424 to Reinhardt disclosed no gravel pack median is used in these extendable ducts. These devices have not been adopted as an accepted practice in the hydrocarbon production because of poor productivity when applied in production wells.
For injection wells poor injectivity can be overcome by exceeding the fracture pressure of the formation as injection rate requirements dictate. By applying a preformed perforation which contains a high strength filter material, sized to prevent formation sloughing, injection well reliability will be greatly improved.
Therefore, there is a need in the art for a method of injection well construction and completion that reliably prevents the formation from sloughing into the injection well borehole, while eliminating internal diameter restrictions associated with the sized screens.